1. Field of the Invention
The present invention relates to a method and apparatus for optically detecting profile errors on a surface of various three-dimensional articles, especially industrial products such as a gear, with respect to the desired profile of a reference surface, by using a coherent beam of light such as a laser beam, and more particularly, it relates to an optical profile error detecting method and an apparatus for carrying out the same, capable of efficiently detecting and measuring profile errors in a plurality of successive inspected surfaces arranged at intervals, such as the flanks of teeth of a gear.
2. Description of the Related Art
A method of three-dimensionally detecting errors in the profile of an inspected article by using a laser beam is disclosed in, for example, U.S. Pat. No. 4,657,396 to Honda et al. In the known method, a laser beam is projected onto the surface of an inspected article at a large angle of incidence, the hologram of a reference surface is irradiated only by the regularly reflected beam of light of the laser beam, the plus first order diffracted wave is focused, the focused condition of the plus first order diffracted beam of light is detected by a photoelectric detecting element, and the profile errors in the surface of the inspected article are measured and detected by analyzing the output signal of the photoelectric detecting element. When the surface of the inspected article is finished by machining, the degree of roughness of such a machined surface is considerably high from the optical point of view, even if the surface is finished to a high precision, and such a machined surface causes light to scatter and makes it difficult to form a hologram. Accordingly, in the foregoing known method, the laser beam is projected at a large angle of incidence on the surface of the inspected article to increase the amount of specularly reflected beam of light by the well-known sheen effect.
However, the foregoing conventional optical profile error detecting method is strictly theoretical and is not practical in application to the measuring and detecting of profile errors on the surface of a detected object or article in industrial manufacture and inspection. For example, a practical constitution of an optical profile error detecting apparatus capable of projecting a signal light beam on a tooth surface at a large angle of incidence and obtaining a specularly reflected beam of light, for efficiently detecting profile errors in the tooth-flanks, for example, of an involute gear by comparing the actual profiles of the tooth-flanks with an ideal involute tooth-flank has not been disclosed. Although the present invention is not limited to the detection of profile errors in the tooth surfaces of gears, it has particularly been desired to develop an optical profile error detecting method and an optical profile error detecting apparatus capable of efficiently detecting errors in the tooth-surfaces of gears including helical gears and skew gears each having a plurality of gear teeth arranged at regular angular intervals.